Solution system for electrolytically removing titanium carbide coating and method for same

ABSTRACT

A solution system for removing titanium carbide coatings on substrate surface by two electrolysis steps is provided. The solution system includes a first electrolyte solution for a first electrolysis step and a second electrolyte solution for a second electrolysis step. The first electrolyte solution contains 2-80 g/L soluble alkali metal hydroxide and 5-100 g/L complexant capable of complexing with titanium ions. The second electrolyte solution contains 50-300 g/L soluble alkali metal hydroxide, 5-100 g/L complexant capable of complexing with titanium ions, and 10-60 g/L alkylol amine. The method for removing titanium carbide coating from the substrate mainly includes two electrolysis steps respectively using the first and second electrolyte solution.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is one of the five related co-pending U.S. patentapplications listed below. All listed applications have the sameassignee. The disclosure of each of the listed applications isincorporated by reference into all the other listed applications.

Attorney Docket No. Title Inventors US 33408 ELECTROLYTE FOR REMOVINGWEI HUANG TITANIUM-CONTAING COATS AND et al. REMOVING METHOD USING SAMEUS 33410 SOLUTION FOR REMOVING TITANIUM- WEI HUANG CONTAINING COATS ANDREMOVING et al. METHOD USING SAME US 33411 SOLUTION FOR REMOVINGTITANIUM- WEI HUANG CONTAINING COATS AND METHOD et al. FOR SAME US 33412SOLUTION FOR ELECTROLYTICALLY WEI HUANG REMOVING CHROMIUM CARBIDE et al.COATING AND METHOD FOR SAME US 33413 SOLUTION SYSTEM FOR ELECTROLYT- WEIHUANG ICALLY REMOVING TITANIUM CARBIDE et al. COATING AND METHOD FORSAME

BACKGROUND

1. Technical Field

The present disclosure relates to a solution system for electrolyticallyremoving titanium carbide coating and a related method.

2. Description of Related Art

Hard ceramic coatings, such as titanium carbide, are widely attached onsurfaces of machining tools and die core-pins. These coatings, however,can fail locally during use or manufacture. Often, when such coatingsfail, the entire component which they are applied is discarded atconsiderable cost even if the underlying substrate shows no damage. Forthis reason, the ability to recycle the underlying substrate by removinga failed coating is economically preferable.

Titanium carbide coating resists wear, abrasion, oxidation, andcorrosion. When manufacturing such coating, the content of carbonincreases with the increasing thickness of the coating to improve thehardness and adjust color of the coating. Electrolytic removal of suchcoating is often carried out using an electrical current density ofhigher than 12A/dm² for a long period of time. However, the underlyingsubstrate may be corroded and this process is very costly.

Therefore, there is room for improvement within the art.

DETAILED DESCRIPTION

The present disclosure relates to a solution system and a related methodfor electrolytically removing titanium carbide coatings formed on thesurfaces of substrates. The substrate may be metal, such as ferric-basedalloy.

The solution system includes a firs electrolyte solution for a firstelectrolysis step and a second electrolyte solution for a secondelectrolysis step.

The first electrolyte solution may be an aqueous solution containing afirst alkali and a first accelerant.

The first alkali may be soluble alkali metal hydroxides, such as, sodiumhydroxide, or potassium hydroxide, or a combination thereof. Theconcentration of the first alkali selected may be about 2-80 g/L, and inthis exemplary embodiment is about 5-50 g/L. The first alkali makes thesolution electrically conductive and providing an alkali condition acidin dissolution of the in the titanium carbide coatings into thesolution.

The first accelerant is a complexant capable of complexing with titaniumions. The first accelerant may be sodium potassium tartrate, sodiumgluconate, sodium citrate, or ethylenediaminetetraacetic acid (EDTA), ora combination thereof. The concentration of the first accelerantselected may be about 5-100 g/L and in this exemplary embodiment isabout 5-40 g/L. The first accelerant can combine with the titanium ionsdissolved in the solution to form coordination compounds and facilitatea continuing dissolution of the titanium ions of the titanium carbidecoating.

The first electrolyte solution may be prepared by dissolving the firstalkali and the first accelerant in water.

The second electrolyte solution may be an aqueous solution containing asecond alkali, a second accelerant, and an auxiliary agent.

The second alkali may be soluble alkali metal hydroxide, such as, sodiumhydroxide, or potassium hydroxide, or a combination thereof. Theconcentration of the second alkali selected may be about 50-300 g/L, andin this exemplary embodiment is about 120-180 g/L. The second alkali mayperform a similar effect with the first alkali of the first electrolytesolution.

The second accelerant is a complexant capable of complexing withtitanium ions. The second accelerant may be sodium potassium tartrate,sodium gluconate, sodium citrate, or EDTA, or a combination thereof. Theconcentration of the second accelerant selected may be about 5-100 g/L,and in this exemplary embodiment is about 5-40 g/L. The secondaccelerant may perform a similar effect with the first accelerant of thefirst electrolyte solution.

The auxiliary agent may be generic alkylol amine capable of combine withtitanium ion. The auxiliary agent may be ethanolamine, diethanolamine,or triethanolamine, or a combination thereof, and preferablytriethavolamine. The concentration of the auxiliary agent selected maybe about 10-60 g/L, and in this exemplary embodiment is about 18-40 g/L.The auxiliary agent may absorb small solid impurities produced duringelectrolysis, preventing the impurities from adhering on the substrate.

The second electrolyte solution may be prepared by dissolving the secondalkali, second accelerant, and auxiliary agent in water.

The method for electrolytically removing the titanium carbide coatingformed on the substrate may include the following steps.

The substrate combined with the coating may be immersed in the firstelectrolyte solution and processed by a first electrolysis step usingthe substrate as the anode. The temperature of the first electrolytesolution during the first electrolysis step is maintained between about50° C. and about 95° C., and in this exemplary embodiment is betweenabout 60° C. and about 80° C. Stainless steel or carbon material may beused as the cathode. The anodic current density is about 1-10A/dm², andin this exemplary embodiment is about 4-7A/dm². The first electrolysisstep takes about 3-8 minutes. After the first electrolysis step, theexterior portion of the coating having a high content of carbide may beremoved. Then, the substrate is rinsed with water and then dried.

The substrate combined with the coating may be immersed in the secondelectrolyte solution and processed by a second electrolysis step usingthe substrate as the anode. The temperature of the second electrolytesolution during the second electrolysis step is maintained between about50° C. and about 95° C., and in this exemplary embodiment is betweenabout 60° C. and about 80° C. Stainless steel or a carbon material maybe used as the cathode. The anodic current density is about 1-10A/dm²,and in this exemplary embodiment is about 4-7A/dm². The secondelectrolysis step takes about 3-8 minutes. After the second electrolysisstep, the remainder titanium carbide coating can be completely removedfrom the substrate.

After the second electrolysis step, the substrate may be rinsed using anaqueous solution containing about 5 wt % sulphuric acid, and then rinsedwith water and dried. The coating can be effectively removed from thesubstrate and the underlying substrate is free from damage.

EXAMPLES

Experimental examples of the present disclosure following.

Example 1

The first electrolyte solution and the second electrolyte solution wereprepared. The first electrolyte solution was an aqueous containing 5 g/Lsodium hydroxide and 10 g/L EDTA. The second electrolyte solution was anaqueous containing 150 g/L sodium hydroxide, 20 g/L sodium potassiumtartrate, and 33 g/L triethanolamine.

Samples of stainless steel substrate having a titanium carbide coatingwere provided. The coatings had a thickness of about 2 μm. The exteriorlayer of the coatings was removed by a first electrolysis step in thefirst electrolyte solution using the substrate as the anode, and usingan anodic current density of about 4A/dm² for about 4 minutes. A pieceof carbon was used as the cathode. The solution was maintained at atemperature of about 60° C. Then, the samples were taken out of thesolution and rinsed with water.

The remainder of the coatings was completely removed by a secondelectrolysis step in the second electrolyte solution using the substrateas the anode, and using an anodic current density of about 5A/dm² forabout 4 minutes. A piece of carbon was used as the cathode. The secondelectrolyte solution was maintained at a temperature of about 80° C.Then, the samples were taken out of the solution and were rinsed withacidic solution and water.

Example 2

Unlike the example 1, the first electrolyte solution was an aqueouscontaining 20 g/L sodium hydroxide and 20 g/L EDTA. The secondelectrolyte solution was an aqueous containing 75 g/L sodium hydroxide,20 g/L sodium citrate, and 28.6 g/L triethanolamine. Except the abovedifference, the remaining experiment conditions of example 2 wererespectively same with example 1.

Example 3

The first electrolyte solution and the second electrolyte solution wereprepared. The first electrolyte solution was an aqueous containing 10g/L sodium hydroxide and 10 g/L sodium gluconate. The second electrolytesolution was an aqueous containing 100 g/L sodium hydroxide, 10 g/Lsodium potassium tartrate, 5 g/L sodium gluconate, and 16.3 g/Ltriethanolamine.

Samples of stainless steel substrate having a titanium carbide coatingwere provided. The coatings had a thickness of about 2 μm. The exteriorlayer of the coatings was partially removed by a first electrolysis stepin the first electrolyte solution using the substrate as the anode, andusing an anodic current density of about 3A/dm² for about 5 minutes. Apiece of carbon was used as the cathode. The solution was maintained ata temperature of about 65° C. Then, the samples were taken out of thesolution and rinsed with water.

The remainder of the coatings was completely removed by a secondelectrolysis step in the second electrolyte solution using the substrateas the anode, and using an anodic current density of about 6A/dm² forabout 5 minutes. A piece of carbon was used as the cathode. The secondelectrolyte solution was maintained at a temperature of about 80° C.Then, the samples were taken out of the solution and were dried afterbeing rinsed with water.

Results of the examples 1-3

The samples processed in the examples 1-3 were inspected by X-raydiffraction (X-RD). No titanium was detected on the samples.Accordingly, the coatings were effectively and completely removed fromthe underlying substrates. Furthermore, the processed samples werescanned using an electron microscope. The scanning indicated nocorrosion found on the underlying substrates.

It should be understood, that the first electrolyte solution or thesecond electrolyte solution may be solely used as the electrolyte forelectrolytically removing the titanium carbide coating by oneelectrolysis step.

It is believed that the present embodiment and its advantages will beunderstood from the foregoing description, and it will be apparent thatvarious changes may be made thereto without departing from the spiritand scope of the disclosure or sacrificing all of its advantages, theexamples hereinbefore described merely being preferred or exemplaryembodiment of the disclosure.

1. An aqueous solution for electrolytically removing titanium carbidecoatings from substrates, comprising: 50-300 g/L soluble alkali metalhydroxide; 5-100 g/L complexant capable of complexing with titaniumions; and 10-60 g/L alkylol amine.
 2. The aqueous solution as claimed inclaim 1, wherein the soluble alkali metal hydroxide is sodium hydroxideor potassium hydroxide, or a combination of the hydroxide and potassiumhydroxide.
 3. The aqueous solution as claimed in claim 2, wherein theconcentration of the soluble alkali metal hydroxide is about 120-180g/L.
 4. The aqueous solution as claimed in claim 1, wherein thecomplexant is selected from one or more of the group consisting ofsodium potassium tartrate, sodium gluconate, sodium citrate,ethylenediamine tetraacetic acid.
 5. The aqueous solution as claimed inclaim 1, wherein the concentration of the complexant is about 5-40 g/L.6. The aqueous solution as claimed in claim 1, wherein the alkylol amineis selected from one or more of the group consisting of ethanolamine,diethanolamine, and triethanolamine
 7. The aqueous solution as claimedin claim 1, wherein the concentration of alkylol amine is about 18-40g/L.
 8. A solution system for removing titanium carbide coatings onsubstrate surface by two electrolysis steps, comprising: a firstelectrolyte solution for a first electrolysis step, the firstelectrolyte solution containing 2-80 g/L soluble alkali metal hydroxideand 5-100 g/L complexant capable of complexing with titanium ions; asecond electrolyte solution a second electrolysis step, the secondelectrolyte solution containing 50-300 g/L soluble alkali metalhydroxide, 5-100 g/L complexant capable of complexing with titaniumions, and 10-60 g/L alkylol amine.
 9. The solution system as claimed inclaim 8, wherein the soluble alkali metal hydroxide in the first andsecond electrolyte solution is sodium hydroxide or potassium hydroxide,or a combination of the hydroxide and potassium hydroxide.
 10. Thesolution system as claimed in claim 9, wherein the concentration of thesoluble alkali metal hydroxide in the first electrolyte solution isabout 5-50 g/L; the concentration of the soluble alkali metal hydroxidein the second electrolyte solution is about 120-180 g/L.
 11. Thesolution system as claimed in claim 8, wherein the complexant in thefirst and second electrolyte solution is selected from one or more ofthe group consisting of sodium potassium tartrate, sodium gluconate,sodium citrate, ethylenediamine tetraacetic acid.
 12. The solutionsystem as claimed in claim 11, wherein the concentration of thecomplexant in the first and second electrolyte solution is about 5-40g/L.
 13. The solution system as claimed in claim 8, wherein the alkylolamine is selected from one or more of the group consisting ofethanolamine, diethanolamine, and triethanolamine.
 14. The solutionsystem as claimed in claim 13, wherein the concentration of the alkylolamine is about 18-40 g/L.
 15. A method for removing a titanium carbidecoating from a substrate, comprising: partially removing the titaniumcarbide coating by a first electrolysis step in a first electrolytesolution using the substrate as the anode, the first electrolytesolution containing containing 2-80 g/L soluble alkali metal hydroxideand 5-100 g/L complexant capable of complexing with titanium ions; andcompletely removing the remainder titanium carbide coating by a secondelectrolysis step in a second electrolyte solution using the substratecombined with the coating as the anode, the second electrolyte solutioncontaining 50-300 g/L soluble alkali metal hydroxide, 5-100 g/Lcomplexant capable of complexing with titanium ions, and 10-60 g/Lalkylol amine.
 16. The method as claimed in claim 15, wherein the anodiccurrent density in the first electrolysis step and second electrolysisstep is about 1-10A/dm²; the first electrolysis step and secondelectrolysis step each takes about 3-8 minutes.
 17. The method asclaimed in claim 16, wherein the first electrolysis step and secondelectrolysis step each continues for about 4-7A/dm².
 18. The method asclaimed in claim 15, wherein the temperature of the first electrolytesolution during the first electrolysis step is maintained between about50° C. and about 95° C.; the temperature of the second electrolytesolution during the second electrolysis step is maintained between about50° C. and about 95° C.
 19. The method as claimed in claim 18, whereinthe temperature of the first electrolyte solution during the firstelectrolysis step is maintained between about 60° C. and about 80° C.;the temperature of the second electrolyte solution during the secondelectrolysis step is maintained between about 60° C. and about 80° C.20. The method as claimed in claim 15, wherein the substrate isferric-based alloy.